Electric circuit breaker



Dec. 26, 1939.

R. E. BOLD ELECTRIC CIRCUIT BREAKER Filed Aug. 1:5, -1938 PigJ.

Insulation TI Inn Vibration Inventor: Ralph E. Bold, b W film/W y His Attorney.

Insulation Patented Dec. 26, 1939 UNITED STATES PATENT OFFICE ELECTRIC CIRCUIT BREAKER York Application August 13, 1938, Serial No. 224,752,

7 Claims.

My invention relates to electric circuit breakers, more particularly to those of the heavy duty type for making and breaking a high voltage power circuit under extreme operating conditions, and has particular application to oil circuit breakers. v Under certain conditions of circuit control, closing of the circuit breaker contacts on a heavy load current often results in burning and deterioration of the contacts. That is, an are forms at the coacting contact surfaces before substantial contact pressure is established, thereby causing melting of the contact material which usually is copper, with resultant formation of high reslstance oxides and gradual deterioration of the contacts themselves. It has been found that this burning action on reclosing is caused to a great extent by rebound or bouncing of the contacts under influence of the usual biasing springs. To

, a certain extent; this bouncing has heretofore been considered a necessary evil since the application of considerable force is required in order to close .the breaker at suflicient speed, and the resilient mounting for providing the usual wipe or overtravel protects the contact structure from mechanical damage due to the closing impact. There is present therefore a tendency for the biased contact to rebound due to the natural period of vibration of its biasing spring.

In accordance with my invention the prime operating essentials are retained and arcing due to bouncing is eliminated by providing separate contacts in multiple having independent resilient mountings that are related to the mass of said contacts so that the rebound periods, thereof are different. Specifically the periodic biasing means such as springs are characterized by different periods of vibration. This is accomplished without impairing the operating speed, contact pressure or current-carrying capacity of the breaker.

My invention will be more fully set forth in the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawing, Fig. 1 is an elevational view of the coacting contact structure of an oil circuit breaker embodying the present invention, and Fig. 2 is an end View of the contact structure shown in Fig. 1.

The circuit breaker illustrated by Fig. l is of the-well-known oil-immersed type, although it should be understood that the present invention is equally applicable to air circuit breakers. in

the specific arrangement shown the relatively movable contact structure comprises a pair of stationary terminals or supports l and 2, on which the fixed contact structure is mounted, and a coacting movable bridging member 3. The bridging member 3 is provided with the usual insulating lift rod 4 for operating the bridging member in reciprocal vertical movement between closed and open circuit positions.

The fixed contact structure at each terminal is substantially identical and comprises main current-carrying contacts 5, which are shown as of the well-known finger type for engaging corresponding wedge-shaped portions 6 of the bridging member. Also mounted on each fixed terminal are two or more butt contact elements 7 and 8 (Fig. 2) serving as arcing contacts. These contacts function both to make and break the circuit, the main current-carrying contacts 5 and 6 being thereby protected from the effects of arcing.

Referring more particularly to Fig. 2, each of the butt contacts 1 and 8 is resiliently mounted for limited movement on the corresponding fixed terminal and to this end, referring specifically to terminal 2, contact I, for example, is provided with a guide stem 9 slidable in the fixed terminal 2. A helical spring I0 is seated between the contact and terminal for biasing the contact toward a lower limiting position that is determined by the collar 9 of the guide pin. The butt contact 8 likewise is similarly biased by a spring I I and the contacts are arranged to be connected in multiple at the terminal 2 by means of flexible conductors l2.

The movable contact structure coacting with each pair of the arcing butt contacts 1 and 8 comprises corresponding butt contact element or elements I3 and Hi suitably mounted, such as by means of a bracket l5, at an end of the bridging member 3. Accordingly, when the lift rod 4 is raised to close the breaker, two pairs of contacts connected in multiple, 1. e., 1-43 and 8-44, engage at each end of the bridging member. The closing operation is accompanied by the usual wipe which results in compression of the springs l0 and Ii. There are therefore provided two shunt paths for the current through the con tacts at each end of the bridging member.

For the purpose of insuring that the circuit is continuous through at least one of these shunt paths upon closing of the breaker, thereby precluding arcing, the resilient period means constituting the springs ii) and II are so related'to the mass of the butt contacts 1 and 8 respectively that the rebound periods at contacts when they are engaged by the bridging member are appreciably difierent. That is, when one butt contact, such as 1, tends to rebound, the other butt contact 8 is in engagement with its coacting contact I4 and, in turn, does not tend to rebound until the contact 1 has again engaged its coacting contact l3. With this arrangement there is provided at least one continuous current path through the contact structure so that there is 10 a minimum of arcing at the reclosing operation. Specifically, this is accomplished in the present instance by providing springs'such as I0 and II that are characterized by different natural periods of vibration. As illustrated the spring I l is heavier and has more mass than the spring Ill and, accordingly, has a different period of vibration than the spring in. This necessarily results in different rebound periods of the contacts I and 8 when the bridging member is raised with considerable force to engage the fixed contacts. The resulting impact, while tending to produce individual bouncing of the contacts, does not reopen the circuit as in previous instances to cause destructive arcing at the contact surfaces by reason of the shunting of the arc current from one butt contact to the other during the brief rebound period.

The method of obtaining different rebound periods of the arcing contacts is subject to variation, and the present invention is not limited to the specific arrangement disclosed. For example, the springs l0 and II may in certain cases be similar and the masses of the butt contact elements 1 and 8 varied instead. In such an arrangement the lower end of each spring would be secured to its corresponding contact so that the natural periods of vibration of the two combinations would be different as in the previous case.

Where differently weighted springs, i. e., 40 springs with different natural periods of vibration, are used it has been found that spring pressures at the separate contacts can vary roughly in the ratio of 3:1. By way of example, in a sample mechanism the spring pressure at one pair of the butt contacts varied from 13 pounds in the open circuit position to 33 pounds in the closed circuit position, and at the other pair in multiple the pressure variation was from 35 pounds in the open circuit position to 85 pounds in the closed circuit position.

It shall be understood that more than two sets or pairs of arcing contacts in multiple can be provided where desired. It has been found, however, that the two shu'nt paths arranged as above described are eifective to reduce arcing to a practically negligible amount on reclosing. The particular arrangement of the resiliently biased contacts is also subject to variation and, by way of example, these contacts can, if desired, be carried on the movable bridging member, or one contact of each pair can be carried on the stationary and movable parts respectively, although the arrangement as illustrated is preferred.

The breaker is also readily applicable to threephase operation, Fig. 2 illustrating an insulatin cross-bar l6 connected with the lift rod 1' for carrying the three bridging members of the usual three-phase breaker.

It should be understood that my invention'is not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without departing from the spirit of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric circuit breaker having relatively movable arcing contact structure comprising a plurality of contact elements adapted to be con- 5 nected in multiple, contact structure coacting therewith for making and breaking the circuit, and resilient periodic means for individually biasing each of said contact elements into contact engagement with said coacting structure so that 10 said elements initially make contact substantially simultaneously, said resilient means being characterized by different natural periods of vibration for each of said contact elements respectively. 16

2. An electric circuit breaker having relatively movable arcing contact structure comprising a plurality of coacting contacts arranged to form at least two pairs "of contacts in multiple, and resilient periodic means for individually biasing 20 one contact of each pair into contact engagement with its coacting contact so that all said contacts initially engage simultaneously, the resilient means for each of said biased contacts being characterized by different natural periods of vi- 25 bration.

3. An electric circuit breaker having relatively movable arcing contact structure comprising a plurality' of contact elements connected in multiple, contact structure coacting therewith, and a 30 spring for individually biasing each of said contacts in multiple into substantially simultaneous contact engagement with said coacting contact structure, said springs being characterized by different natural periods of vibration. 35

4. An electric circuit breaker having relatively movable arcing contact structure comprising a plurality of contact elements arranged to form at least two pairs in multiple, and a spring for biasing one contact of each pair into substantial- 40 ly simultaneous contact engagement with the corresponding coacting contact, said springs being related to the mass of said biased contacts so that there is an appreciable difierence in the rebound period of said biased contacts. 48

5. An electric circuit breaker having relatively movable arcing contact structure comprising a stationary support, a plurality of contact elements connected in multiple mounted on said support, movable contact structure coacting with 60 each of said contact elements at substantially the same time for making and breaking the circuit and a spring adapted to be compressed by said movable structure for individually biasing each of said contact elements into contact en- 88 gagement with said movable structure in the closed circuit position, said springs being related to said contact elements so as to produce appreciably different rebound periods of said contact elements during the circuit closing operation. 00

6. An electric circuit breaker having relatively movable arcing contact structure comprising a stationary support, a pair of butt contacts conlnected in multiple and mounted for limited movement on said support, movable butt contact structure for engaging at substantially the same time each of said fixed butt contacts, and spring means adapted to be compressed by said movable structure for individually biasing each of said fixed butt contacts into engagement in the closed circuit position, said springs having different periods of vibration for varying the rebound period of said fixed butt contacts.

7. An electric circuit breaker having relatively movable arcing contact structure comprising a ll pair of stationary supports, a pair of butt contacts connected in multiple and slidably mounted on each of said supports, a separate spring for individually biasing each of said butt contacts towards a limiting position with respect to said supports, and a movable bridging member having butt contact surfaces for engaging at the same time each of said fixed butt contacts so that said springs are compressed in the closed circuit position, the spring of each fixed butt contact being related to the mass of said contact so that said fixed butt contacts have difierent rebound periods when engaged by the coacting butt 6 contacts of said movable bridging member.

RALPH E. BOLD. 

